Wasn't sure where to post this since it's more of a design question than a rules question, but:

It appears that a standard Prosthetic Limb provides precisely zero benefit compared to a natural limb. Given that, I don't really get why it takes up two augmentation slots. Which means that a character with a prosthetic leg can't ever have Speed Suspension or Force Soles, for example, and a character with two prosthetic arms cannot ever have Force Palms or a Polyhand.

Additionally, a Storage limb is just a Hideaway Limb and a Prosthetic Limb put together, for an extra 1200 credits on top of the regular cost of those two items. Just... Why?

Well, if you lose a limb and don't replace it with a prosthetic, you're not putting anything in those slots anyway, and you'd still be missing a limb. So there's that.

Dracomicron wrote:

100 credits is a pittance next to the Regenerate spell.

I'd rather have an arm for cheap than not have an arm for nothing.

Granted, but the entry for a prosthetic limb could just as easily state "other augmentations may be installed in this limb as though it were a natural limb", possibly with a limitation preventing Biotech. So, why doesn't it? It's a decision that doesn't make sense to me.

Well, if you lose a limb and don't replace it with a prosthetic, you're not putting anything in those slots anyway, and you'd still be missing a limb. So there's that.

Dracomicron wrote:

100 credits is a pittance next to the Regenerate spell.

I'd rather have an arm for cheap than not have an arm for nothing.

Granted, but the entry for a prosthetic limb could just as easily state "other augmentations may be installed in this limb as though it were a natural limb", possibly with a limitation preventing Biotech. So, why doesn't it? It's a decision that doesn't make sense to me.

I had the same quibble when I lost my hand to an infernal Hellknight. All of the augmentations in the core book could be used in prosthetics except I think the Venom Spur because of special text allowing it in each augmentation individually. I thought, "Why not just say that prosthetics can install other augments?"

The answer is future proofing. They don't want to invalidate Regeneration (the spell or table), and they knew that they would eventually release more augments that don't mention being able to install them in prosthetic limbs. So there is still an incentive to go out and grow your own limb back through expensive procedures... you get your augmentation slots back.

There's also fancier prosthetic limbs out there now. I'm not sure it would be okay to install extra augmentations in a weaponized prosthesis.

As for the Storage Limb's bizarre price bump... yeah I dunno. That baffled me as well. I guess you can technically install an extra augmentation in the Storage Limb if it can be installed in prosthetics, whereas Hideaway Limb isn't considered a prosthetic and won't stack. That's all I can think of.

The answer is future proofing. They don't want to invalidate Regeneration (the spell or table), and they knew that they would eventually release more augments that don't mention being able to install them in prosthetic limbs. So there is still an incentive to go out and grow your own limb back through expensive procedures... you get your augmentation slots back.

Which just leads me to the question of why there isn't a conceptual space around replacement limbs as a potential advantage, but that might be my Shadowrun showing.

Yeah, it doesn't really seem like an even distribution as far as cost vs what the replacement limb actually does. My guess is they had the ideas for cybernetic limbs first, and just kind of guessed at price points for prosthetic limbs.

The answer is future proofing. They don't want to invalidate Regeneration (the spell or table), and they knew that they would eventually release more augments that don't mention being able to install them in prosthetic limbs. So there is still an incentive to go out and grow your own limb back through expensive procedures... you get your augmentation slots back.

Which just leads me to the question of why there isn't a conceptual space around replacement limbs as a potential advantage, but that might be my Shadowrun showing.

Well, the advantage is that you get whatever bonus the augmentation has, if any. The basic 100 credit version's benefit is "You can tie your shoes unassisted." Weaponized Prosthesis's advantage is "You are a walking pronk-stick of death." the Bone Blade arm necrograft's advantage is "I am so pointy now" and "I can be healed by Necromantic Revitalization."

There's plenty of space for Shadowrun-style enhancement, but you have to take into consideration that the stat math in Starfinder is very tight; you can't just hand out extra +2 to Strength or something for having a bionic arm without fragging the game balance.

Relevant rules for folks:
Necrograft Subtype
Adding even a single necrograft to a living body causes the recipient creature to gain the necrograft subtype. Abilities, items, and spells that detect or identify undead reveal necrografts (identifying only the augmentations as undead, rather than the recipient creature as a whole).

Creatures with this subtype are also damaged by spells that damage undead and can be subjected to other undead-specific effects. If a spell or ability that does something other than deal damage would not normally affect such a creature but does affect undead, it can affect a creature with the necrograft subtype, but that creature gains a bonus to its AC and saving throw against the effect equal to 4 – the number of necrografts it has (to a minimum bonus of +0).

It does seem silly that because I have a black heart implant, I can be healed as if I was actually undead. I wouldn't be surprised if a GM didn't allow it, though I wouldn't be happy. I'd also expect the door to swing both ways, and things that harm or hinder only undead wouldn't work on me either.

the Bone Blade arm necrograft's advantage is "I am so pointy now" and "I can be healed by Necromantic Revitalization."

You found a GM who allows that? Crazy.

It's the text of the rules...

Necrograft Subtype: ...if a spell or ability that does something other than deal damage would not normally affect such a creature, but does affect undead, the creature can be targeted, but it gains a bonus to its AC and saving throw against the efffect equal to 4 - the number of necrografts it has, (to a minimum bonus of +0).

Necromantic Revitalization doesn't do damage, has a separate effect that affects undead but not other creatures, does not require an attack roll, and is listed as "(harmless)" in its save section.

I don't see why it wouldn't heal someone with a necrograft. Nothing about the Necrograft subtype says that it has to be a purely negative trait.

The answer is future proofing. They don't want to invalidate Regeneration (the spell or table), and they knew that they would eventually release more augments that don't mention being able to install them in prosthetic limbs. So there is still an incentive to go out and grow your own limb back through expensive procedures... you get your augmentation slots back.

Which just leads me to the question of why there isn't a conceptual space around replacement limbs as a potential advantage, but that might be my Shadowrun showing.

Well, the advantage is that you get whatever bonus the augmentation has, if any. The basic 100 credit version's benefit is "You can tie your shoes unassisted." Weaponized Prosthesis's advantage is "You are a walking pronk-stick of death." the Bone Blade arm necrograft's advantage is "I am so pointy now" and "I can be healed by Necromantic Revitalization."

There's plenty of space for Shadowrun-style enhancement, but you have to take into consideration that the stat math in Starfinder is very tight; you can't just hand out extra +2 to Strength or something for having a bionic arm without fragging the game balance.

Straight up stat bonuses are definitely not a great plan there, but I think there's a lot of room for things like Technomancer/Mechanic abilities to temporarily amp up the prosthetic, as well as to have things which benefit class features of the more technological classes, or to have improvements to certain skills/applications of skills...

Shadowrun's system works on the basis that the limb almost definitely starts off worse than your natural limb, and you have to invest to make it even be just as good as a natural limb, much less better (and there are larger costs in the form of Essence loss) - so they can afford in terms of power budget to have something as strong as stat bonuses.

It’s clearly intended to be a negative balancing trait (thus the save bonus that declines as you add more) and didn’t foresee necromantic revitalization being written and other effects where you’d waive a save.

It’s clearly intended to be a negative balancing trait (thus the save bonus that declines as you add more) and didn’t foresee necromantic revitalization being written and other effects where you’d waive a save.

Interestingly, it does open up the ability for a Technomancer to work as a party healer if everyone takes at least one Necrograft.

Though technomancers do have a couple other ways to access self-healing, at least.

It’s clearly intended to be a negative balancing trait (thus the save bonus that declines as you add more) and didn’t foresee necromantic revitalization being written and other effects where you’d waive a save.

Interestingly, it does open up the ability for a Technomancer to work as a party healer if everyone takes at least one Necrograft.

Though technomancers do have a couple other ways to access self-healing, at least.

Given that they relaxed the "worst" language on androids and construct targeting to mean "most permissive" for purposes of things like Mending I guess this might be in line with intent after all.

It’s clearly intended to be a negative balancing trait (thus the save bonus that declines as you add more) and didn’t foresee necromantic revitalization being written and other effects where you’d waive a save.

Interestingly, it does open up the ability for a Technomancer to work as a party healer if everyone takes at least one Necrograft.

Though technomancers do have a couple other ways to access self-healing, at least.

Given that they relaxed the "worst" language on androids and construct targeting to mean "most permissive" for purposes of things like Mending I guess this might be in line with intent after all.

It’s clearly intended to be a negative balancing trait (thus the save bonus that declines as you add more) and didn’t foresee necromantic revitalization being written and other effects where you’d waive a save.

I thought that at first too, but the spell came out in Pact Worlds and necrografts are in the armory.

I know there's plenty of evidence that Paizo Writer B clearly didn't read what Paizo Writer A put in a book, but at some point you've just got to draw a line and use what we have.

I thought it was basically just flavor that cost you a few credits to be able to look cool and call yourself a cyborg.

Seems highly unintuitive to me that androids and SROs can benefit from augmentations, but not cyborgs with prosthetics.

You need a rule saying you can augment prosthetic limbs. Prosthetic limbs occupy slots, and only one thing can occupy a slot at a time without a special rule allowing it. For example, there are special rules allowing speed suspensions (legs), swimming fins (feet), and climbing suckers (feet) to be installed in prosthetic legs. But there is no similar wording for Force Soles, so those can only go in your original feet.

It’s clearly intended to be a negative balancing trait (thus the save bonus that declines as you add more) and didn’t foresee necromantic revitalization being written and other effects where you’d waive a save.

I thought that at first too, but the spell came out in Pact Worlds and necrografts are in the armory.

I know there's plenty of evidence that Paizo Writer B clearly didn't read what Paizo Writer A put in a book, but at some point you've just got to draw a line and use what we have.

It’s clearly intended to be a negative balancing trait (thus the save bonus that declines as you add more) and didn’t foresee necromantic revitalization being written and other effects where you’d waive a save.

I think the Starfinder writers aren't losing any sleep over another incentive to stuff yourself full of freaky 'ware. Be cool, be undead, whatever man.

There's a squick factor in necrografts, but apart from that, it's really not such a big downside as it might seem. Sure, you can be attacked by stuff that works only on undead. But how often do you face an enemy with those powers, that couldn't also spend its actions and spell slots on things that would mess up a purely alive PC?